Defibrillator Display

ABSTRACT

Systems and methods related to the field of cardiac resuscitation, and in particular to devices for assisting rescuers in performing cardio-pulmonary resuscitation (CPR) are described herein.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to U.S. Provisional Application Ser.No. 61/304,119, filed on Feb. 12, 2010, entitled “DEFIBRILLATORCHARGING,” and U.S. Provisional Application Ser. No. 61/307,690, filedon Feb. 24, 2010, entitled “DEFIBRILLATOR DISPLAY,” the entire contentsof each of which are hereby incorporated by reference.

TECHNICAL FIELD

This document relates to cardiac resuscitation, and in particular tosystems and techniques for assisting rescuers in performingcardio-pulmonary resuscitation (CPR).

BACKGROUND

The heart relies on an organized sequence of electrical impulses to beateffectively. Deviations from this normal sequence is known as“arrhythmia.” Certain medical devices include signal processing softwarethat analyzes electrocardiography (ECG) signals acquired from a medicalpatient (e.g., a victim at a scene of an emergency) to determine when acardiac arrhythmia such as ventricular fibrillation (VF) or shockableventricular tachycardia (VT) exists. These devices include automatedexternal defibrillators (AEDs), ECG rhythm classifiers, and ventriculararrhythmia detectors. An AED is a defibrillator—a device that deliverscontrolled electrical shock to a patient—while being relatively easy touse, such as by providing verbal prompts to a provider of care to “talk”the provider through a process of evaluating a patient for, attachingthe patient to, and activating, AED therapy. Certain of the medicaldevices just discussed are also capable of recognizing the two distinctcardiac waveforms: VT and VF.

VT is a tachydysrhythmia that originates from a ventricular ectopicfocus, characterized by a rate that is typically greater than 120 beatsper minute and wide QRS complexes. VT may be monomorphic (typicallyregular rhythm originating from a single focus with identical QRScomplexes) or polymorphic (unstable, may be irregular rhythm, withvarying QRS complexes). An example rhythm for an unstable VT isillustrated in FIG. 1A. Depending on the rate and the length of timethat the VT has been sustained, a heart in the VT state may or may notproduce a pulse (i.e., pulsatile movement of blood through thecirculatory system). The cardiac activity in the VT state still has somesense of organization (note that the “loops” are all basically the samesize and shape). If there is no pulse associated with this VT rhythm,then the VT is considered to be unstable and a life threateningcondition. An unstable VT can be treated with an electrical shock ordefibrillation.

Supraventricular tachycardia (SVT) is a rapid heartbeat that beginsabove the heart's lower chambers (the ventricles). SVT is an abnormallyfast heart rhythm that begins in one of the upper chambers of the heart(atria), a component of the heart's electrical conduction system calledthe atrioventricular (AV) node, or both. Although SVT is rarelylife-threatening, its symptoms, which include a feeling of a racingheart, fluttering or pounding in the chest or extra heartbeats(palpitations), or dizziness can be uncomfortable.

VF is usually an immediate life threat. VF is a pulseless arrhythmiawith irregular and chaotic electrical activity and ventricularcontraction in which the heart immediately loses its ability to functionas a pump. VF is the primary cause of sudden cardiac death (SCD). Anexample rhythm for VF is illustrated in FIG. 1B. This waveform does nothave a pulse associated with it. There is no organization to this rhythm(note the irregular size and shape of the loops). The pumping part ofthe heart is quivering like a bag of worms, and it is highly unlikelythat this activity will move any blood. The corrective action for thisrhythm is to defibrillate the heart using an electrical charge.

A normal heart beat wave starts at the sinoatrial node (SA node) andprogresses toward the far lower corner of the left ventricle. A massiveelectrical shock to the heart can correct the VF and unstable VTrhythms. This massive electrical shock can force all the cardiac cellsin the heart to depolarize at the same time. Subsequently, all of thecardiac cells go into a short resting period. The hope is that thesinoatrial node (SA node) will recover from this shock before any of theother cells, and that the resulting rhythm will be a pulse-producingrhythm, if not normal sinus rhythm.

Many AEDs implement algorithms to recognize the VT and VF waveforms byperforming ECG analyses at specific times during a rescue event of apatient using defibrillation and cardio-pulmonary resuscitation (CPR).The first ECG analysis is usually initiated within a few seconds afterthe defibrillation electrodes are attached to the patient. SubsequentECG analyses may or may not be initiated, based upon the results of thefirst analysis. Typically, if the first analysis detects a shockablerhythm, the rescuer is advised to deliver a defibrillation shock.Following the shock delivery, a second analysis can be initiatedautomatically to determine whether the defibrillation treatment wassuccessful or not (i.e., the shockable ECG rhythm has been converted toa normal or other non-shockable rhythm). If this second analysis detectsthe continuing presence of a shockable arrhythmia, the AED advises theuser to deliver a second defibrillation treatment. A third ECG analysismay then be executed to determine whether the second shock was or wasnot effective. If a shockable rhythm persists, the rescuer is thenadvised to deliver a third defibrillation treatment.

Following the third defibrillator shock or when any of the analysesdescribed above detects a non-shockable rhythm, treatment protocolsrecommended by the American Heart Association and European ResuscitationCouncil require the rescuer to check the patient's pulse or to evaluatethe patient for signs of circulation. If no pulse or signs ofcirculation are present, the rescuer can be directed to perform CPR onthe victim for a period of one or more minutes. The CPR includes rescuebreathing and chest compressions. Following this period of CPR, the AEDreinitiates a series of up to three additional ECG analyses interspersedwith appropriate defibrillation treatments as described above. Thesequence of three ECG analyses/defibrillation shocks followed by 1-3minutes of CPR, continues in a repetitive fashion for as long as theAED's power is turned on and the patient is connected to the AED device.Typically, the AED provides audio prompts to inform the rescuer whenanalyses are about to begin, what the analysis results were, and when tostart and stop the delivery of CPR.

Many studies have reported that the discontinuation of precordialcompression can significantly reduce the recovery rate of spontaneouscirculation and 24-hour survival rate for victims. Thus, it is useful torecognize abnormal heart rhythms during chest compressions. There isrecent clinical evidence showing that performing chest compressionsbefore defibrillating the patient under some circumstances can bebeneficial. Specifically, it is clinically beneficial to treat a patientwith chest compressions before defibrillation if the response times ofthe medical emergency system result in a delay of more than fourminutes, such that the patient is in cardiac arrest for more than fourminutes. Chest compression artifact rejection can employ spectralanalysis of the ECG, defibrillation success prediction, and therapeuticdecision-making typically specify a set of parameters in the ECGfrequency spectrum to be detected. For example, U.S. Pat. No. 5,683,424compares a centroid or a median frequency or a peak power frequency froma calculated frequency spectrum of the ECG to thresholds to determine ifa defibrillating shock is necessary.

Unfortunately, existing AEDs require batteries able to deliver largeamounts of current due to the charging requirements of defibrillatorhigh voltage capacitors. This results in batteries that are excessive inboth size and weight that limit both their portability, convenience, andin the case of external, wearable defibrillators such as the LifeVest(ZOLL Medical, Chelmsford, Mass.) their wearability and comfort. Inaddition, batteries continue to be the least reliable element of theAEDs currently manufactured, with regular recalls resulting frommanufacturing defects as well as normal end-of-life degradation thatalways occurs with batteries, but are particularly troublesome forlife-saving equipment.

SUMMARY

This document describes systems and techniques that may be used toprovide information about patient status during the use of adefibrillator device. The systems and techniques described herein aim toidentify the most important data and to display the information in anefficient and effective manner to a rescuer. The data displayed to therescuer can change based on the actions of the rescuer. For example, thedata displayed can differ based on whether the rescuer is currentlyadministering CPR chest compressions to the patient. The data about thepatient is presented graphically and textually in a manner that improvesthe ability of a rescuer to quickly understand the state of a patientand to make clinical decisions that will benefit the patient. Forexample, during CPR chest compressions, information about the chestcompressions including rate and depth is displayed on the same displaydevice as a filtered ECG waveform and CO2 or SpO2 waveform. The displayof such information in one location provides the advantage of giving therescuer needed information about the patient in one convenient locationin an easy to view formal. In certain implementations, additionalinformation about the quality of the CPR chest compressions can bepresented to the rescuer such as a release indicator.

In certain implementations, such systems and technique may provide oneor more advantages. For example, patient care may be improved when arescuer can easily view well-formatted information in a single location.Also, rescuers may be able to modify their administration of CPR to bemore effective because they have been presented relevant data in anunderstandable manner.

In one implementation, a method for monitoring patient activity using anexternal defibrillator includes obtaining data regarding chestcompressions performed on the patient, determining values for depth andrate of a plurality of the chest compressions, and displaying on agraphical display screen of the defibrillator, indications of thedetermined values for depth and rate.

Embodiments can include one or more of the following.

Determining the values for depth and rate can include determiningnumeric values in terms of distance for depth and compressions perminute for rate, and wherein displaying the indications of thedetermined values for depth and rate comprises displaying numbers thatcorrespond to the determined numeric values.

The method can also include displaying an icon adjacent the indicationsof the determined values that indicates whether the chest compressionsare being performed properly. A color of the icon can change based onwhether the chest compressions are being performed properly orimproperly.

The method can also include receiving information about the patient'sheart activity and displaying on the graphical display, with thedetermined values for depth and rate, an electrocardiogram of thepatient. Displaying the electrocardiogram can include moving anelectrocardiogram trace laterally across the display. The method canalso include displaying an unfiltered electrocardiogram, sensing thatchest compressions have commenced on the patient, and subsequentlydisplaying a filtered electrocardiogram. The method can also includemomentarily displaying on a trace of the electrocardiogram, anunfiltered portion showing compression artifacts, between anotherunfiltered portion and a filtered portion.

The method can also include displaying second data from the patient incoordination with the electrocardiogram. The method can also includechanging a source of the second data in response to sensing that chestcompressions have commenced on the patient. Changing the source of thesecond data can include changing from SPO2 to CO2. Changing the sourceof the second data can include changing from a patient chemicalmeasurement to a chest compression measurement. The chest compressionmeasurement can be displayed in the form of a bar graph. Lengths of barsin the bar graph can represent compression depths and spacing of bars inthe bar graph represent compression rate. The method can also includedisplaying indicators for standard depth and rate with the bar graph.

Obtaining the data regarding chest compressions performed on the patientcan include obtaining measurements from an accelerometer that ispositioned to move in coordination with the patient's breastbone.Determining a value for depth can include double integratingmeasurements from the accelerometer. The accelerometer can be attachedto a housing that is in turn attached to a pair of defibrillatorelectrodes to be placed on the patient.

In another implementation, an external defibrillator includes one ormore sensors arranged to contact a patient and obtain measurementsregarding chest compressions performed on the patient, a video displayscreen for displaying graphical representations regarding status of thepatient and the defibrillator to a rescuer, and a processor connected tomemory that stores computer instructions for determining values of depthand rate of chest compressions performed on the patient and sensed bythe sensors, and causing the video display screen to display indicationsof the determined values for depth and rate.

Embodiments can include one or more of the following.

The instructions for determining the values for depth and rate caninclude instructions for determining numeric values in terms of distancefor depth and compressions per minute for rate, and wherein displayingthe indications of the determined values for depth and rate comprisesdisplaying numbers that correspond to the determined numeric values. Theinstructions can be further provided to cause the video display screento display an icon adjacent the indications of the determined valuesthat indicates whether the chest compressions are being performedproperly. A color of the icon changes based on whether the chestcompressions are being performed properly or improperly.

The instructions can be further provided to cause the display on thevideo display screen an electrocardiogram of the patient with thedetermined values for depth and rate, in response to receivinginformation about the patient's heart activity. Displaying theelectrocardiogram can include moving an electrocardiogram tracelaterally across the display. The instructions can be further providedto cause the display on the video display screen of an unfilteredelectrocardiogram, and the subsequent display of a filteredelectrocardiogram upon sensing that chest compressions have commenced onthe patient. The instructions can be further provided to momentarilydisplay on a trace of the electrocardiogram, an unfiltered portionshowing compression artifacts, between another unfiltered portion and afiltered portion. The instructions can be further provided to displaysecond data from the patient in coordination with the electrocardiogram.The instructions can be further provided to change a source of thesecond data in response to sensing that chest compressions havecommenced on the patient. Changing the source of the second data caninclude changing from SPO2 to CO2. Changing the source of the seconddata can include changing from a patient chemical measurement to a chestcompression measurement.

The chest compression measurement can be displayed in the form of a bargraph. Lengths of bars in the bar graph can represent compression depthsand spacing of bars in the bar graph represent compression rate. Theinstructions can further be provided to display indicators for standarddepth and rate with the bar graph. Obtaining the data regarding chestcompressions performed on the patient can include obtaining measurementsfrom an accelerometer that is positioned to move in coordination withthe patient's breastbone. Determining a value for depth can includedouble integrating measurements from the accelerometer.

The one or more sensors can include an accelerometer that is attached toa housing that is in turn attached to a pair of defibrillator electrodesto be placed on the patient.

In one implementation, an external defibrillator includes one or moresensors arranged to contact a patient and obtain measurements regardingchest compressions performed on the patient, a video display screen fordisplaying graphical representations regarding status of the patient andthe defibrillator to a rescuer, and means for determining values ofdepth and rate of the chest compressions and for causing the videodisplay screen to display indications of the determined values for depthand rate in response to receiving data from the one or more sensors thatindicates the depth and rate of the chest compressions.

Other features and advantages will be apparent from the description anddrawings, and from the claims.

DESCRIPTION OF DRAWINGS

FIG. 1A is a magnitude versus time plot of a ventricular tachycardia(VT) rhythm.

FIG. 1B is a magnitude versus time plot of a ventricular fibrillation(VF) rhythm.

FIG. 2 is a diagram of one implementation including an automaticelectronic defibrillator (AED) and a multiple lead electrocardiograph(ECG) device.

FIG. 2A is a diagram of the AED of FIG. 2.

FIGS. 3A and 3B are examples of ECG analysis and charging cycles.

FIG. 4A is a flow chart showing actions taken to charge a defibrillationdevice during chest compressions associated with a CPR interval.

FIG. 4B is a flow chart showing actions taken to charge a defibrillationdevice using different current levels that are selected based on thelikelihood of a shockable rhythm being observed.

FIG. 4C is a flow chart showing actions taken to adaptively charge adefibrillation device using different current levels based on thelikelihood of a shockable rhythm being observed.

FIG. 4D is a flow chart showing actions taken to adaptively charge adefibrillation device to a level selected based on ECG analysis.

FIG. 5A is a diagram of and ECG signal.

FIG. 5B is a diagram of a CPR acceleration signal showing strongcross-correlation with the ECG signal.

FIG. 6A is a diagram of and ECG signal.

FIG. 6B is a diagram of a CPR acceleration signal showing lowcross-correlation with the ECG signal.

FIG. 7 is a diagram of a defibrillation device with a display.

FIG. 8A is a flow chart showing actions taken to modify informationpresented on a display of a defibrillation device based on the detectionof CPR chest compressions.

FIGS. 8B-8E are screenshots showing exemplary information presented on adefibrillator display.

FIG. 9A is a flow chart showing actions taken to provide an indicationof CPR quality on a display of a defibrillator device.

FIGS. 9B and 9C are screenshots showing exemplary information presentedon a defibrillator display.

FIG. 10A is a flow chart showing actions taken to provide a releaseindicator.

FIGS. 10B and 10C are screenshots showing exemplary informationpresented on a defibrillator display.

FIG. 11 is a screenshot showing exemplary information presented on adefibrillator display.

DETAILED DESCRIPTION

This description discusses systems and techniques for providingdefibrillation energy in a controlled manner. In general, such energyneeds to be built up, such as by charging a capacitor, and that build upof energy may take an appreciable length of time. Using the techniquesdiscussed here, a system can analyze a patient's needs in advance of thetime to delivery defibrillation pulse (e.g., while a rescuer isperforming chest compressions) and can begin charging a capacitor orother appropriate energy delivery mechanism sufficiently in advance ofthe time that a shock will be needed, so that the shock can be deliveredas soon as it is needed.

Referring now to FIG. 2, an AED 10 is shown that may be used to providea defibrillation shock at an appropriate time. In the figure, whichshows an example implementation, a rescuer uses an AED 10 toautomatically monitor a victim during cardiac resuscitation. The AED 10uses measured ECG signals to monitor the victim's heart, and charges thedefibrillation device within the AED while the victim is resuscitatedusing chest compressions techniques. In some examples, the manner inwhich the defibrillation device is charged (e.g., the rate of charge,the total amount of charge stored) can be based on the measured ECGsignals. Advantageously, charging the defibrillation device during CPRchest compressions reduces the amount of time that the victim is notreceiving chest compressions because, if a shockable rhythm exists, thedevice is armed and ready to deliver the shock as soon as the rescuercompletes the chest compressions.

The AED 10 includes a speaker 16, a display screen 18, ananalog-to-digital converter 20, a processor 22, and a defibrillatorpulse generator 24. The analog-to-digital converter 20 is connected to aset of ECG leads that are in turn attached to the victim. The ECG leadspass signals to the processor 22 for monitoring the electrical rhythmsof the victim's heart. The converter 20 sends the signals from the ECGleads to the processor 22. The processor 22 monitors the victim's heartfor dangerous rhythms using the ECG signals while the victim isresuscitated using chest compressions techniques.

If the AED 10 detects a dangerous heart rhythm, the AED 10 generates analarm signal. The alarm signal is noticeable to the rescuer. The AED 10can generate a defibrillating shock to the victim when the rescuerissues a command to the AED 10 directing such a shock. Thedefibrillating shock is intended to remedy the dangerous rhythm of thevictim's heart.

The AED 10 also includes a charging module 19 that is configured tocharge the AED during chest compressions. The module 19 can adaptivelycharge the AED based on monitored ECG signals. In some examples, thedefibrillator is pre-charged only if a shockable rhythm is likely toexist as determined by analysis of the monitored ECG signals. In someadditional examples, the level of charge for the device is determinedand set based on the monitored ECG signals. In some additional examples,the method of charging (e.g., the rate of charge) varies based on themonitored ECG signals in an effort to conserve power. For example, iftime allows, a capacitor may be charged more slowly than it normallywould in order to conserve power, but still ensure that the capacitorwill reach its full charge just as the defibrillator is needed by therescuer.

The AED 10 uses a rhythm advisory method for a) quantifying thefrequency-domain features of the ECG signals; b) differentiating normaland abnormal ECG rhythms, such as VF; c) detecting the onset of abnormalECG rhythms; and d) making decisions about the physiological states ofthe heart. This frequency-domain measure can be reliable with or withoutthe presence of the chest compression artifact in the ECG signals. TheAED 10, after identifying the current physiological state of the heart,can make a decision about appropriate therapeutic action for the rescuerto make and communicate the action to the rescuer using the speaker 16and the display screen 18.

The AED 10 may incorporate functionality for performing additionaltherapeutic actions such as chest compressions, ventilations, ordelivery of intravenous solution-containing metabolic or constitutivenutrients. Based on the results of the analysis of the rhythm advisorymethod, the AED 10 may automatically deliver the appropriate therapy tothe patient.

The AED 10 may also be configured in “advisory” mode wherein the AED 10will prompt the caregiver after the AED 10 has made a determination ofthe best therapy, and acknowledgement by the caregiver/device operator,in the form of a button press or voice-detected acknowledgement, isrequired before therapy is delivered to the patient.

The AED 10 analyzes the ECG signals to predict defibrillation success aswell as to decide whether it is appropriate to defibrillate or todeliver an alternative therapy such as chest compressions, drugs such asepinephrine, constitutive nutrients such as glucose, or other electricaltherapy such as pacing.

In some examples, one or more therapeutic delivery devices 30automatically deliver the appropriate therapy to the patient. Thetherapeutic delivery devices 30 can be, for example, a portable chestcompression device, a drug infusion device, a ventilator and/or a devicethat includes multiple therapies such as defibrillation, chestcompression, ventilation and drug infusion. The therapeutic deliverydevices 30 are physically separate from the defibrillator AED 10, andcontrol of the therapeutic delivery devices 30 may be accomplished by acommunications link 32. The communications link 32 may take the form ofa cable but preferably the link 32 is via a wireless protocol.

In other examples, control and coordination for the overallresuscitation event and the delivery of the various therapies may beaccomplished by a device 34 or processing element that is external tothe AED 10. For instance, the device 34 may download and process the ECGdata from the AED 10; analyze the ECG signals, perform relevantdeterminations like those discussed above and below based on theanalysis, and control the other therapeutic devices 30, including theAED 10. In other examples, the AED 10 may perform all the processing ofthe ECG, including analyzing the ECG signals, and may transmit to thecontrol device 34 only the final determination of the appropriatetherapy, whereupon the control device 34 would perform the controlactions on the other linked devices 30.

Chest compression artifacts can be separated from the ECG signalcomponents, making it possible for the AED 10 to process the ECG signalwithout halting the processing during chest compressions. Exemplarymethods for analyzing the ECG signal to determine if a shockable rhythmexists are described, for example, in U.S. Pat. No. 7,565,194, titled“ECG Rhythm Advisory Method,” the contents of which are herebyincorporated by reference in their entirety.

It has been recognized that good chest compressions during CPR isessential to saving more victims of cardiac arrest. The compression raterecommended by the American Heart Association in its guidelines isgreater than 100 compressions per minute. Many studies have reportedthat the discontinuation of chest compressions, such as is commonly donefor ECG analysis and charging of a defibrillator, can significantlyreduce the recovery rate of spontaneous circulation and 24-hour survivalrate. Because of safety issues with delivery of a high voltagedefibrillation shocks with voltages of 1000-2000 volts, rescuers aretaught to cease chest compressions and remove their hands from thevictim's chest before initiating the defibrillation shock. By analyzingECG signals during chest compressions as a mechanisms to permit earliercharging of an energy delivery device (e.g., a capacitor) in adefibrillator device, the gaps in providing chest compressions can bereduced, and patient care increased.

FIG. 3A shows an example of an ECG analysis and charging cycle in whichcharging of a defibrillator device starts after a CPR interval hasended. As shown in the figure, in operation of some AED devices, therescuer is instructed to perform chest compressions for a two minute CPRinterval 300 after which the rescuer is instructed to pause his or herperformance of CPR 304. At this point, the rescuer removes his or herhands from the victim, ECG analysis is performed, and the defibrillatordevice is charged (interval 302). As such, a time period elapses (timeperiod 302) during which the rescuer is not delivering chestcompressions to the victim. This elapsed time period before delivery ofthe shock 307 can be, for example, about 10 seconds—of which a portionis devoted to performing the ECG analysis and a portion is devoted tocharging the defibrillation device. While methods exist for processingECG signals without halting the processing during CPR chestcompressions, a time period may still elapse between the cessation ofchest compressions and availability of an adequate charge for deliveringa shock.

FIG. 3B shows an example of an ECG analysis and charging cycle in whichcharging of a defibrillator device starts before a CPR interval hasended. The CPR interval can be based on a length of time ofadministration of chest compressions (e.g., as shown in FIG. 3B), atotal number of chest compressions, a total number of effective chestcompressions based on depth or rate of the compression, a total lengthof time of effective chest compressions, or can be variable based on oneor more observed factors such as the ECG analysis. The CPR interval canadditionally be updated by software or firmware to handle different CPRprotocols such that the device is charged and the defibrillation therapyis delivered according to the protocol. As shown in the figure, inoperation methods described herein, the defibrillation device is chargedwhile the rescuer is providing the CPR chest compressions. Similar tothe method described with respect to FIG. 3A, the rescuer is instructedto perform chest compressions for a two minute CPR interval 308. Duringthe two minute CPR interval, ECG analysis is performed and thedefibrillator device is charged (interval 310). After the CPR intervalis complete, the rescuer is instructed to pause CPR 312, and shock 314can be delivered almost immediately to the victim because thedefibrillator device has already had time to charge. Because thedefibrillator device is fully charged before the rescuer ceases chestcompressions, the time period during which the rescuer is not deliveringchest compressions to the victim can be greatly reduced and the shockcan be delivered immediately or almost immediately after chestcompressions are completed. For example, the elapsed time between theend of the CPR interval and the delivery of the shock (if a shockablerhythm exists) can be less than about 5 seconds (e.g., less than about 5seconds, less than about 3 seconds, less than about 2 seconds, less thanabout 1 second, less than about ½ a second). In some embodiments, thelength of time between the rescuer ceasing chest compressions anddelivery of the shock can be simply based on the amount of time therescuer spends locating and pressing a button on the AED device thatcauses the AED device to deliver the shock to the victim.

In some additional embodiments, the AED device may utilize a briefperiod of time (e.g., while the rescuer locates and presses the button)after the rescuer ceases chest compressions to reconfirm thedesirability of delivering the shock to the victim. For example, arescuer can be instructed to visually inspect and confirm that ashockable rhythm exists and/or the AED device can continue to collectand analyze ECG signals (in the absence of chest compressions resultingin less artifacts in the ECG signal) to re-confirm the desirability ofdelivering the shock. In general, a time period for re-confirmationbased on analysis of an ECG signal without chest compression artifactscan be brief (e.g., less than about 5 seconds, less than about 3seconds, less than about 2 seconds). The time period for re-confirmationcan be based on physiological characteristics (e.g., heart rate that isfast or slow) and/or a desired confidence level for the ECG analysis.

Because of safety issues with charging the defibrillation device to avoltage of 1000-2000 volts while the rescuer is in contact with thevictim, safety interlocks can be included in a defibrillator device toensure that the voltage is not discharged before the rescuer removes hisor her hands from the victim. The defibrillator safety interlocks caninclude one or more software-controlled-hardware and/or softwaremechanisms that prevent the defibrillator from accidentally dischargingoutside of the unit. In order for the defibrillator to deliver a shock,the AED device confirms that a variety of software and hardware statesare met during the charging process. Once the defibrillator reaches afull level of charge, a therapy button is enabled. Enabling the therapybutton removes a final hardware safety interlock and selects the outputfor the therapy charge to the patient connector instead of the internalresistor network used to dissipate charge when a shock is not delivered.Once enabled, a rescuer presses the therapy button and the AED registersthe press which closes a therapy delivery relay and delivers thedefibrillation pulse. The safety interlocks control the enablement ofthe therapy button and a do not allow the rescuer to deliver a shock tothe victim until other actions occur that disable the safety interlocks.

In some additional methods, an electrically insulating protection layerextends over the surface of the patient so that manual compressions maycontinue safely and unabated during the charging of the defibrillationdevice and delivery of the defibrillation shock. An exemplaryelectrically insulating protection layer is described, for example, inU.S. Pat. No. 6,360,125, which is incorporated by reference herein inits entirety.

In some embodiments, the period for administration of chest compressionsis not preset, rather the period can be variable based on the observedEGC signals. ECG analysis may start while CPR chest compressions arebeing administered. When the AED device determines that a shockablerhythm exists based on the ECG signals or otherwise makes adetermination that the appropriate therapy would be to deliver thedefibrillation shock, the AED device can begin charging. CPR chestcompressions continue while the device is charging. The AED device canoptionally instruct the rescuer of an amount of time that he/she shouldcontinue to administer chest compressions based on the length of timeused to charge the defibrillator device. Once the device is fullycharged, the rescuer can be instructed to pause chest compressions andthe shock can be delivered almost immediately to the victim.

FIG. 4A is a flow chart showing actions taken to charge a defibrillationdevice during chest compressions associated with a CPR interval. Asnoted above, charging the defibrillation device in addition to analyzingan ECG signal during chest compressions can provide the advantage ofreducing the amount of time that a rescuer is not administering chestcompressions to the victim. In general, an interval (e.g., a set lengthof time) is set for the administration of chest compressions. Duringthis interval, the system analyzes an ECG signal and charges thedefibrillation device. Safety interlocks are enabled that preventaccidental dissipation of the charge in the defibrillation device duringthe CPR chest compression interval. At the end of the CPR interval, adecision of whether to shock the victim is made based on the ECG signalanalysis, and the stored charge is either administered to the victim ordissipated internally.

The example process here begins at box 402, where the AED analyzes anECG signal to determine if a shockable rhythm is present in the victim.The ECG signal is measured while chest compressions are beingadministered to the victim. As such, the AED separates the chestcompression artifact from the ECG signal components to process the ECGsignal without halting the processing during CPR chest compressions(e.g., as described in U.S. Pat. No. 7,565,194).

At box 404, the AED determines if the current time is near the end ofthe CPR interval (e.g., within about 10-30 seconds of the end of the CPRinterval). Exemplary CPR intervals can be between 2 and 5 minutes (e.g.,2 minutes, 3 minutes, 4 minutes, and 5 minutes). If the current timewithin a determined window for performing chest compressions is not nearthe end of the CPR interval, the AED device continues to analyze the ECGsignals (box 402). If the current time is near the end of the CPRinterval, the AED enables safety interlocks at box 406 (though theinterlocks may be enabled even before this time).

As the chest compressions continue, the AED begins charging thedefibrillation device at box 408 with the safety interlocks enabled. Theamount of time needed to charge the defibrillation device can vary basedon the current used to charge the device and the total amount of chargedesired. As such, the system begins charging the defibrillation devicein advance of the end of the CPR interval such that the defibrillationdevice will be fully charged at the end of the CPR interval. Forexample, a window for performing CPR can be determined when the CPRcycle begins, a time for charging the defibrillation device can belooked up or otherwise determined, and the system may be programmed tocheck, at a time in advance of the end of the window that substantiallycorresponds to the charging time, for whether a shockable rhythm ispresent

At box 410, the AED performs a final analysis of the ECG signal todetermine if a shockable rhythm is present in the victim. Exemplarymethods for analyzing the ECG signal to determine if a shockable rhythmexists are described, for example, in U.S. Pat. No. 7,565,194, titled“ECG Rhythm Advisory Method,” the contents of which are herebyincorporated by reference in their entirety. If a shockable rhythm isnot observed, at box 422, the AED instructs the rescuer to continuechest compressions. Thus, if a shockable rhythm does not exist, thevictim receives uninterrupted chest compressions. Such chestcompressions may not place the heart back into normal operation, butthey may nonetheless maximize perfusion of blood through the heart untila more highly-trained rescuer can arrive and take over.

At box 424, the AED dissipates the charge from the defibrillation devicewithout delivering a shock to the victim. For example, the AED candissipate the stored charge using a resistor network inside the AEDdevice such that the charge can be dissipated without requiring therescuer to discontinue chest compressions. The dissipation may occur bydumping the charge, for example. The charge may also be “recycled” backinto a battery on the device so as to extend the battery life.

If a shockable rhythm is observed, at box 414, the AED device instructsthe rescuer to discontinue chest compressions. For example, the AEDdevice can provide audible instructions to the rescuer via a speakerand/or can provide a visual instruction to the rescuer via a displaydevice. At box 416, the AED disables the safety interlocks, thus makingit possible for the shock to be delivered through electrodes that areattached to the victim.

At box 418, the AED device delivers the defibrillation shock to thevictim. Such delivery may occur in response to the rescuer pressing abutton on the AED to provide a command to delivered the shock. The shockmay also be delivered automatically, such as after the AED voices acommand to stand clear of the victim. The shock is delivered withoutsignificant delay after the cessation of chest compressions because thedevice has been previously pre-charged while the chest compressions werebeing administered.

At box 420, the AED device instructs the user to resume chestcompressions. This initiates another CPR cycle during which a similarECG analysis will be performed. The process just described may thus berepeated until a shock succeeds in placing the victim's heart roughlyback into a normal operating mode, or until additional caregivers arriveto attempt different resuscitation approaches.

In some embodiments, a reconfirmation of the desirability to deliver thedefibrillation shock to the victim is performed after the rescuer ceaseschest compressions. Because the re-confirmation is performed when therescuer is not delivering chest compressions, the ECG signals analyzedby the AED device during the reconfirmation are expected to be lessnoisy and have less artifacts because artifacts from the chestcompressions are no longer present. As such, an ECG analysis may havehigher degree of confidence. In general, as described above, a timeperiod for re-confirmation based on analysis of an ECG signal withoutchest compression artifacts can be brief (e.g., less than about 5seconds, less than about 3 seconds, less than about 2 seconds).

In some embodiments, the AED device can determine whether to perform areconfirmation analysis based on one or more factors associated with theprior EGC analysis such as a certainty value. For example, if the priorEGC analysis results in a high certainty that delivering thedefibrillation shock to the victim is the appropriate therapy (e.g., ahigh certainty of conversion to a perfusing rhythm) then the AED maydeliver the shock nearly immediately after the rescuer ceases chestcompressions (e.g. without a reconfirmation period). On the other hand,if the prior EGC analysis has a lower certainty that delivering thedefibrillation shock to the victim is the appropriate therapy then theAED may perform a reconfirmation analysis before making a finaldetermination of whether to deliver the defibrillation shock.Additionally or alternatively a determination of whether to perform areconfirmation analysis can be based on a confidence value associatedwith the level of confidence that the EGC signal analysis is correct.For example, if the signal is extremely noisy and has a large presenceof artifacts, the confidence of the analysis may be lower making itdesirable to reconfirm the analysis in the absence of the chestcompressions.

FIG. 4B is a flow chart showing actions taken to charge a defibrillationdevice using different current levels that are selected based on thelikelihood of a shockable rhythm being observed. Portable AED devicesmay be powered by a battery or other power supply having a limitedlifetime. In order to conserve power for future uses of the AED deviceor for the administration of multiple shocks to a single victim, variouscharging algorithms can be used. In some examples, an AED device makes adetermination of whether a shockable rhythm exists in the victim andonly charges the defibrillator device if a shockable rhythm exists. Sucha charging algorithm conserves power because if a shockable rhythm isnot observed, the AED device does not charge the defibrillator and thendump or dissipate the charge.

The example process begins at box 425, where the AED analyzes an ECGsignal while chest compressions are being administered to a victim todetermine if a shockable rhythm is likely to be present in the victim atthe end of the CPR interval (e.g., as described in U.S. Pat. No.7,565,194). At box 426, the AED determines if a shockable rhythm islikely to be present in the victim at the end of the CPR interval. Whilethe CPR interval will continue regardless of the outcome of theanalysis, the determination is used to decide whether to begin chargingthe defibrillator device. The time at which to make such a determinationmay be set by a determination of how long it will take to charge thedefibrillator device. When different possible rates of charge areavailable to the system, and maximum time charge can be set for the ECGanalysis, a rate of charge may be determined, and then the actualcharging may begin at a time preceding the end of CPR that issubstantially the amount of time the charge will take at the computedrate of charge.

A threshold for determining whether to pre-charge the defibrillator canbe different from a threshold used to determine whether to administer ashock to the victim. For example, because the determination is used todecide whether to pre-charge the AED device, a lower threshold may beused such that the device will be fully charged at the end of the CPRinterval if a shock may be administered. For example, an accuracymeasure can be used to set the thresholds. For example, an observedsignal resulting in a high accuracy value (e.g., a confidence of greaterthan about 90%) can be used as to set a threshold for determiningwhether to administer a defibrillation shock to the victim while a lowerconfidence (e.g., a confidence of 50% or greater) can be used to set athreshold for determining whether to begin charging the defibrillationdevice. For example, an AMSA number that is associated with a certainaccuracy level in predicting a successful conversion can be used to setthe thresholds for deciding whether to pre-charge the defibrillator, therate of charging the defibrillator, and whether to administer thedefibrillation shock. This AMSA number can be customized based on arequest of the rescuer or the medical director. For example, an AMSAnumber that is associated with a accuracy level of 90% or greater (e.g.,90% or 95%) in predicting a successful conversion can be used to set thethreshold for administering a defibrillation shock and an AMSA numberthat is associated with a accuracy level of 70% or greater (e.g., 70%,80%, 90%) in predicting a successful conversion can be used to set thethreshold for deciding whether to pre-charge the defibrillator. In otherexamples, an AMSA number that is associated with an accuracy level of70% or greater (e.g., 70%, 80%, 90%) in predicting a successfulconversion can be associated with the fastest possible rate in chargingthe defibrillator; The lower value the AMSA number is, the rate ofcharging is set to (e.g., half speed in charging when an AMSA numberassociated with an accuracy level of 50% is observed). In someembodiments, other predictors of conversion success (e.g., SCE) can beused.

If a shockable rhythm is not likely to be present in the victim at theend of the CPR interval, the AED continues to receive and analyze theECG signals. At box 428 near the end of the CPR cycle, the AED deviceperforms a final analysis of the ECG signal to determine whether ashockable rhythm exists. This second determination of whether ashockable rhythm exists serves as a confirmation that a shockable rhythmstill does not exist, so that a rescuer does not forego providing ashock to the victim in a situation where the patient's condition haschanged in a manner that would make a shock would be beneficial.

In contrast, if the system determines that a shockable rhythm is likelyto exist, at box 427, the AED pre-charges the defibrillation device.This charging occurs while the rescuer is administering the CPR chestcompressions. At box 428 near the end of the CPR cycle, the AED deviceperforms a final analysis of the ECG signal.

At box 429, the AED device determines whether a shockable rhythm exists.This second determination of whether a shockable rhythm exists serves asa confirmation that a shockable rhythm still exists, so that a rescueris not led to give a shock to a patient when the patient's condition haschanged in a manner that would make the shock essentially futile. Adifferent threshold can be used for the determination of whether toadminister the shock to the victim than was used to determine whether topre-charge the defibrillator.

If a shockable rhythm does not exist at this later time and under thislater standard (though the standard may also be the same for decidingwhether to pre-charge and deciding whether to remove the safetyinterlocks and allow the shock actually to be delivered), the AEDinstructs the rescuer to continue chest compressions at box 434 suchthat the victim receives uninterrupted chest compressions. At box 435,the AED dissipates the charge (e.g., using one or more of the methodsdescribed herein) from the defibrillation device without delivering ashock to the victim if the device was pre-charged (e.g., at box 427).

If a shockable rhythm is observed, at box 430, the AED device determineswhether the defibrillator was pre-charged (e.g., at box 427) and chargesthe defibrillator if it was not previously pre-charged (or completes anystill-incomplete charging). At box 431, the AED device instructs therescuer to discontinue chest compressions (e.g., using one or more ofthe methods described herein). At box 432, the AED device delivers theshock and at box 432, the AED device instructs the user to resume chestcompressions. This initiates another CPR cycle during which a similarECG analysis will be performed.

FIG. 4C is a flow chart showing actions taken to charge a defibrillationdevice using different current levels based on the likelihood of ashockable rhythm being observed. One exemplary way to conserve power inan AED is to charge the AED device at a lower current over a longerperiod of time (e.g., over a period of at least 30 seconds), resultingin less of a drain on the batter power as compared to charging the AEDdevice to the same total charge using a higher current and a shorterperiod of time (e.g., over a period of at most 10 seconds). A percentagecalculated by dividing the lower charging current by the higher chargingcurrent can be greater than about 50% (e.g., greater than about 50%,greater than about 60%, greater than about 75%) and less than about 90%(e.g., less than about 90%, less than about 80%).

Charging the AED device over a longer period of time at a lower currentcan occur during the CPR interval because the typical CPR interval isbetween 2-5 minutes. Both charging the device at a lower current (thatis selected to permit full or substantially full charging during theavailable charging interval before a shock may be needed) and/or onlycharging the device if it is likely that a shock will be administered tothe victim can contribute to an extended battery life for the AEDdevice. Drawing less total current from the battery can provideadditional advantages such as enabling the use of a smaller battery (andthereby enabling a smaller and lighter AED) and/or enabling the use ofalternative power devices such as solar power and/or human generatedpower.

In one embodiment, a “crank” generator may be employed. Since the timeavailable to charge the defibrillator capacitor can be increased to asmuch as 3-10 minutes using the systems and methods described herein, a200 joule capacitor only requires at most approximately a 1.5 watt powersource, assuming a 3 minute charge duration and a high voltage flybackcircuitry efficiency of 75%. Due to leakage of a typical film capacitorat maximum voltage of approximately 2 Watts, a generator of 2.5-3 Wattswould be required. Such a power supply may be an external hand crankpower supply available commercially (SuperBattery with Crank Generator,Teledex, Inc., N.J.), or a built-in crank generator in the defibrillatorwith a power output sufficient to charge the defibrillator capacitor inthe allotted time. As part of the generator, an additional energystorage element will preferably be included, for instance a battery ascontained in the Superbattery described above, or a so-called“ultracapacitor”, such as that manufactured by Maxwell Technologies (SanDiego), for instance the 350 Farad, part number BCAP0350 E270 T11. Theultracapacitor is used to maintain power for the low-voltage circuitrysuch as signal amplifiers and digital processing circuitry when therescuer has stopped providing mechanical energy to the generator. Themechanical energy for the generator may alternatively be contained in astructure positioned on the patient's sternum, which will be compressedduring cardiopulmonary resuscitation. Currently, devices existcommercially (CPR-STATPADZ, ZOLL Medical, Chelmsford, Mass.) whichmeasure the performance of the rescuer doing chest compressions bymeasuring the compression depth via an accelerometer sensor within alow-profile housing positioned under the rescuers hands while they arecompressing the patient's sternum during CPR. The housing mayadditionally be constructed to flexibly deform during sternalcompressions, thus causing motion of the actuator of a generator, forinstance a linear motion electric power generator as described in U.S.Pat. No. 5,818,132. A typical patient requires approximately 100 poundsof force to depress the sternum to the required depth of 2 inches, asper the American Heart Association recommendations. Thus, by allowingfor a deformation of the housing of 0.5-1 inches would increase thecompression depth of the rescuer to 2.5-3 inches to achieve the samesternal depth of 2 inches, but would provide the requisite 2.5-3 Wattsof necessary power, assuming a generator efficiency of 40%.Alternatively, the housing may be a spring-loaded two piece housing withaccelerometer and generator contained within the housing, the upperportion of the generator actuator affixed to the upper portion of thehousing, the generator and the lower portion of the actuator affixed tothe lower housing, and power generated when the spacing between theupper and lower housings is changed.

In another embodiment, the lid of the AED might be surfaced with a solarcell, thus providing approximately 100 square inches of availablesurface area. Standard, commercially available amorphous Silicon crystalcells currently provide approximately 45 milliwatts per inch squared.This power can be doubled by employing a more expensive crystalline cellas well as alternative structures. Thus, the solar cell would be able toprovide 4-10 Watts of power, which is more than sufficient for thesystems and methods described herein. As with the human poweredgenerator approach, an electrical energy storage element would beincluded, such as an ultracapacitor, in addition to the defibrillatorcapacitor, for powering the analog and digital low-voltage electronics,if for instance a shadow from the rescuer passes in front of the solarcells during device use. Thus, even with batteries that have failed orwhose performance has degraded to the point that they are unable topower the defibrillator, it is now possible to have a backup powersource for use in emergencies, not currently available with existingtechnology. In the preferred embodiment, a fail-safe switch, relay ortransistor would be employed that would disconnect the failed batteriesfrom the electronics, so that power would not be diverted from thegenerator or solar cell by the batteries during operation.

Because the defibrillator capacitor can be charged over a significantlyincreased period of time, the peak charging current is significantlydecreased by a factor of ten or more. This allows for significantlysmaller batteries to be used to power the defibrillator. This allows forsignificantly smaller batteries to be used to power the defibrillator.In general, the batteries can include one or more primary cells and/orone or more secondary (e.g., rechargeable) cells. Examples ofsignificantly smaller batteries that can be used to power thedefibrillator include any battery (or combination of multiple batteries)with a relatively low power output of, for example, less than about 10 W(e.g., less than about 10 W, less than about 7 W, less than about 5 W,less than about 4 W, less than about 3 W). In some examples, the poweroutput can be greater than about 2.5 W and less than 10 W (e.g., betweenabout 2.5 W and about 10 W, between about 2.5 W and about 7 W, betweenabout 2.5 W and about 5 W, between about 2.5 W and about 4 W, betweenabout 2.5 W and about 3 W). In one particular example, the current ZOLLAEDPlus requires ten lithium CR123 commercial batteries to power thedefibrillator, at a significant size, weight and cost expense. With thesystems and methods described herein, this can be reduced to 1, or atmost, 2 CR123 batteries. In addition, it is now possible to use evensmaller alkaline batteries, such as a standard commercially-available‘C’ size alkaline cell.

At box 436, while chest compressions are being administered, the AEDanalyzes an ECG signal (e.g., as described in U.S. Pat. No. 7,565,194)and at box 437, the AED determines if a shockable rhythm is likely to bepresent in the victim at the end of the CPR interval. While the CPRinterval will continue regardless of the outcome of the analysis, thedetermination is used to decide whether to begin charging thedefibrillator device.

If a shockable rhythm is not likely to be present in the victim at theend of the CPR interval, the AED continues to receive and analyze theECG signals. At box 439, near the end of the CPR cycle, the AED performsa final analysis of the ECG signal to determine whether a shockablerhythm exists. The analysis may also continue until a shockable rhythmis present.

In contrast, if the system determines that a shockable rhythm is likelyto exist (either initially or upon further monitoring and analysis), atbox 438, the AED device begins pre-charging the defibrillation device ata low charging current. In other examples, the charging current can bebased on the length of time remaining in the CPR interval. For example,a charging current can be selected such that the device will be fullycharged at the end of the CPR interval. This may result in the chargingoccurring at a low rate over an extended period of time (e.g., over aperiod of time greater than about 30 seconds, over a period of timegreater than about 45 seconds, over a period of time greater than about1 minute). For example, if a shockable rhythm is determined initially,the charging rate may be relatively low, whereas if there was no initialshockable rhythm but the device senses a shockable rhythm later in thechest compression cycle, the charging rate may be relatively fast. Thischarging occurs while the rescuer is administering the CPR chestcompressions (though some may occur after the end of the provision ofCPR chest compressions, though not enough that it would create ansubstantial effect on the timing of the CPR).

At box 439 near the end of the CPR cycle, the AED device performs afinal analysis of the ECG signal, and at box 440, the AED devicedetermines whether a shockable rhythm exists. If a shockable rhythm doesnot exist, the AED instructs the rescuer to continue chest compressionsat box 450 such that the victim receives uninterrupted chestcompressions. At box 452, the AED dissipates the charge (e.g., using oneor more of the methods described herein) from the defibrillation devicewithout delivering a shock to the victim if the device was pre-charged(e.g., at box 438).

If a shockable rhythm is observed, at box 441, the AED device determineswhether the defibrillator has reached a full level of charge and chargesthe defibrillator to the full level of charge (if needed) at a highcurrent. For example, while the pre-charging can occur at a low currentover an extended period of time, charging to reach the full charge ifthe device is not fully charged in time (or charging if not pre-charged)can occur at a high current and during as short of period as ispractical.

At box 444, the AED device instructs the rescuer to discontinue chestcompressions (e.g., using one or more of the methods described herein).At box 446, the AED device delivers the shock and at box 448, the AEDdevice instructs the user to resume chest compressions. This initiatesanother CPR cycle during which a similar ECG analysis will be performed.

FIG. 4D is a flow chart showing actions taken to adaptively charge adefibrillation device to a level (e.g., a desired total voltage orcharge) selected based on ECG analysis. For example, a level of chargefor the defibrillation device (and a total amount of charge delivered tothe victim) can be adaptively determined based on factors related to theECG analysis such as the amplitude, frequency of the ECG signal, and/oran AMSA value. For example, if a victim is experiencing VF with a highamplitude ECG signal, only a low level of energy in the shock may beused. In contrast, in situations where it is not likely that conversionto a perfusing rhythm will occur with only a low energy shock such assituations in which the ECG signal exhibits a low amplitude, then thedefibrillation device can be charged to a higher energy level.

In some implementations, an amplitude magnitude spectrum area (AMSA)value can be used to determine how to charge the defibrillation deviceand when to administer a defibrillation shock. For example, a high AMSAvalue is believed to be correlated to a high likelihood of conversion toa perfusing rhythm. The AMSA value can be monitored and the level ofshock and/or length of time chest compressions are administered can bemodified based on a threshold AMSA value and/or trends observed in theAMSA value. For example, a shock could be administered when a change(e.g., a decrease) in the AMSA value is observed by systems provided inan AED device. The AMSA value can also be used to determine the rate incharging the defibrillator. For example, an AMSA number that isassociated with an accuracy level of 70% or greater (e.g., 70%, 80%,90%) in predicting a successful conversion can be associated with thefastest possible rate in charging the defibrillator; The lower value theAMSA number is, the rate of charging is set to (e.g., half speed incharging when an AMSA number associated with an accuracy level of 50% isobserved).

In FIG. 4D at block 462, while chest compressions are beingadministered, the AED device analyzes an ECG signal, and at box 464, theAED device determines if a shockable rhythm is likely to be present inthe victim at the end of the CPR interval. If a shockable rhythm is notlikely to be present in the victim at the end of the CPR interval, theAED instructs the rescuer to continue chest compressions for another CPRinterval at box 468 and continues to receive and analyze the ECGsignals. If the system determines that a shockable rhythm is likely toexist, at box 466, the AED device determines a level of charge based onan analysis of the ECG signal. For example, the level of charge or therate of charging can be based on an amplitude of the ECG signal, afrequency of the ECG signal, and/or and AMSA value of the ECG signal.The level of charge can vary from a low charge to a high charge. Ingeneral, if the AMSA value is used, the level of charge is proportionalto the AMSA value such that the device is charged to a higher level ifthe AMSA value is higher. At box 470, the AED charges the defibrillationdevice to the determined level of charge. The rate of charging can alsovary from a slow charging rate to a fast charging rate: for example, ifthe AMSA value is used, the charging rate can be proportional to theAMSA value such that the device is charged faster if the AMSA value ishigher.

At box 472, near the end of the CPR interval, the AED device performs afinal analysis and determines (box 474) if a shockable rhythm ispresent. If a shockable rhythm does not exist, the AED instructs therescuer to continue chest compressions at box 482 such that the victimreceives uninterrupted chest compressions. At box 483, the AEDdissipates the charge (e.g., using one or more of the methods describedherein) from the defibrillation device without delivering a shock to thevictim.

If a shockable rhythm is observed, at box 476, the AED instructs therescuer to discontinue chest compressions (e.g., using one or more ofthe methods described herein). At box 478, the AED device delivers theshock and at box 480, the AED device instructs the user to resume chestcompressions.

Other data besides ECG data may be included as part of the determinationof whether a shockable rhythm exists and may be incorporated into theanalysis algorithm, for instance pulse oximetry, capnography,respiration, impedance cardiography, and blood pressure measurements. Atleast some of the data may remain in the time domain without any Fourieror other transform method being performed on it. Pulse oximetry,impedance cardiography, and blood pressure measurements may be used toaugment the ECG to determine if a pulse is present. Capnography may beused to determine the overall effectiveness of cardiopulmonaryresuscitation. The additional measures can also include measurement ofvelocity or acceleration of chest compression during chest compressionsaccording to the techniques taught by U.S. Pat. No. 7,220,335, Methodand Apparatus for Enhancement of Chest Compressions During ChestCompressions, the contents of which are hereby incorporated by referencein their entirety and U.S. patent application Ser. No. 11/430,579 titledECG rhythm advisory method the contents of which are hereby incorporatedby reference in their entirety.

In some embodiments, the cross-correlation between the ECG signal (withCPR artifact) and the CPR signal (in the form of compressionacceleration, velocity, or displacement) can be calculated. Based on thestrength of the cross-correlation between the ECG signal and the CPRsignal, the system can select an appropriate analysis method to removethe artifacts from the ECG signal and determining if a shockable rhythmexists in the ECG signal. For example, a high cross-correlation valuebetween the ECG signal and the CPR signal indicates that the majority ofthe artifact is from the chest compression and thus an analysis methoddesigned for ECG with CPR artifact may be more reliable than otheranalysis methods. Alternatively, a low cross-correlation value typicallyindicates that there is strong non-CPR-related artifact in the recordedECG signal.

FIGS. 5A and 5B illustrate an example of the observed ECG signal (FIG.5A) showing strong cross-correlation with the CPR acceleration signal(FIG. 5A), which indicates that the ECG signal is free from non-CPRnoise. The strong cross correlation can be observed based on thesimilarity in the shape of the CPR signal and the ECG signal. The crosscorrelation can be computed automatically during the analysis of the ECGsignal.

As noted above, a low cross-correlation value between the ECG signal andthe CPR signal typically indicates that there is strong non-CPR-relatedartifact in the recorded ECG signal. With the presence of thenon-CPR-related artifact, the ECG analysis performed during CPR may beless reliable (or may not be reliable). Due to the lesser reliability ofthe ECG analysis, the system can utilize a longer period of CPR-freetime in a re-confirmation analysis (e.g., a longer analysis period canbe utilized after the cessation of CPR and prior to the determination ofwhether a shockable rhythm exists). FIGS. 6A and 6B illustrate anexample of the observed ECG signal (FIG. 6A) with weak cross-correlationwith the CPR acceleration signal (FIG. 6B). This indicates that the ECGhas strong non-CPR noise and a longer of re-confirmation analysis periodcan be used.

The information processing technique can include but is not limited tosimple combining rules or math, neural networks, expert systemsincorporating fuzzy or standard logic, or other artificial intelligencetechniques. For example, multiple factors can be combined to make adetermination of whether to defibrillate. In some situations, even if ashockable rhythm exists (e.g., as determined based on the ECG analysis)the AED device may not recommend delivering the shock to the patientbecause one or more other factors suggest that another treatment wouldlikely be more effective. For example, if a shockable rhythm exists butthe quality of CPR chest compressions as measured based on one or moreof the velocity, acceleration, or depth of the compressions is low, thenthe AED device could recommend continuing chest compressions to increaseblood circulation rather than stopping the chest compressions to deliverthe shock.

In some embodiments, the AED device can combine different measures andoutput results related to the desirability of defibrillation and/or theeffectiveness of the chest compressions being delivered by the rescuer.Exemplary outputs can include statements such as “strong need fordefibrillation,” “weak need for defibrillation,” “faster chestcompressions needed,” or “additional chest compressions needed.”

In some embodiments, the AED device can deliver the defibrillation shockduring the chest compression cycle (e.g., while the rescuer isdelivering the chest compressions). For example, the AED can synchronizeof the defibrillation shock to the chest compression cycle. Delivery ofthe defibrillation shock during the early portion (approximately thefirst 300 milliseconds) of the decompression (diastolic) phase of thechest compression cycle can improve the likelihood of success of thedelivered shock. The decompression phase begins when the rescuer reducescompression force on the chest, allowing the chest to rise, and theheart to expand. The AED device can detect chest compression phase andtiming information indicative of the start of the decompression phaseand initiate delivery of the electromagnetic therapy within 300milliseconds of the start of the decompression phase. In someembodiments, delivery of electromagnetic therapy can be initiated within25-250 milliseconds of the start of the decompression phase. Circuitryand processing for the detection of chest compression phase timinginformation can include a pressure sensor and/or an accelerometer.Exemplary methods for synchronizing defibrillation with chestcompression phase are described in U.S. patent application Ser. No.12/263,813 titled Synchronization of Defibrillation and ChestCompressions, the contents of which are hereby incorporated by referencein their entirety.

Large self-adhesive electrode pads (˜5″ in diameter) are typically usedto deliver defibrillation therapy to patients. The pads also provide ECGmonitoring through the conductive surfaces that deliver therapy. In oneimplementation, additional small (˜0.5″ diameter) ECG electrodes can beintegrated into the large pads.

In one embodiment, the two small ECG electrodes and large pads areconfigured such that there at least two mutually orthogonal ECG leadsare generated. The vector sum of these leads generates a trajectory overtime. The same methods for trajectory analysis described above may beused to analyze this trajectory as well.

FIG. 7 shows a defibrillation device 500 with a display portion 502 thatprovides information about patient status and CPR administration qualityduring the use of the defibrillator device. The data is collected anddisplayed in an efficient and effective manner to a rescuer. As shown ondisplay 502, during the administration of chest compressions, the device500 displays information about the chest compressions in box 514 on thesame display as a filtered ECG waveform 510 and a CO2 waveform 512(alternatively an SpO2 waveform can be displayed).

During chest compressions, the ECG waveform is generated by gatheringECG data point and accelerometer readings and filtering the motioninduced (e.g., CPR induced) noise from the ECG waveform. Measurement ofvelocity or acceleration of chest compression during chest compressionscan be performed according to the techniques taught by U.S. Pat. No.7,220,335, Method and Apparatus for Enhancement of Chest CompressionsDuring Chest Compressions, the contents of which are hereby incorporatedby reference in their entirety. Displaying the filtered ECG waveformhelps clinicians reduce interruptions in CPR because the displayedwaveform is easier for the rescuer to decipher. If the ECG waveform isnot filtered, artifacts from manual chest compressions make it difficultto discern the presence of an organized heart rhythm unless compressionsare halted. Filtering out this artifact allows clinicians to view theunderlying rhythm without stopping chest compressions.

The CPR information in box 514 is automatically displayed whencompressions are detected. The information about the chest compressionsdisplayed in box 514 includes rate 518 (e.g., number of compressions perminute) and depth 516 (e.g., depth of compressions in inches ormillimeters). The rate and depth of compressions can be determined byanalyzing accelerometer readings. Displaying the actual rate and depthdata (in addition to or instead of an indication of whether the valuesare within or outside of an acceptable range) is believed to provideuseful feedback to the rescuer. For example, if an acceptable range forchest compression depth is between 1.5-2 inches, providing the rescuerwith an indication that his/her compressions are only 0.5 inches canallow the rescuer to determine how to correctly modify his/heradministration of the chest compressions.

The information about the chest compressions displayed in box 514 alsoincludes a perfusion performance indicator (PPI) 520. The PPI 520 is ashape (e.g., a diamond) with the amount of fill in the shape differingto provide feedback about both the rate and depth of the compressions.When CPR is being performed adequately, for example, at a rate of about100 compressions/minute (CPM) with the depth of each compression greaterthan 1.5 inches, the entire indicator will be filled. As the rate and/ordepth decreases below acceptable limits, the amount of fill lessens. ThePPI 520 provides a visual indication of the quality of the CPR such thatthe rescuer can aim to keep the PPI 520 completely filled.

As shown in display 500, the filtered ECG waveform 510 is a full lengthwaveform filling the entire span of the display device while the secondwaveform (e.g., the CO2 waveform 512) is a partial length waveform andfills only a portion of the display. A portion of the display beside thesecond waveform provides the CPR information in box 514. For example,the display splits the horizontal area for the second waveform in half,displaying waveform 512 on left and CPR information on the right in box514.

The data displayed to the rescuer can change based on the actions of therescuer. For example, the data displayed can differ based on whether therescuer is currently administering CPR chest compressions to thepatient. Additionally, the ECG data displayed to the user can changebased on the detection of CPR chest compressions. For example, theadaptive filter can automatically turn ON or OFF based on detection ofwhether CPR is currently being performed. When the filter is on (duringchest compressions), the filtered ECG data is displayed and when thefilter is off (during periods when chest compressions are not beingadministered) unfiltered ECG data is displayed. An indication of whetherthe filtered or unfiltered ECG data is displayed can be included withthe waveform.

FIG. 8A is a flow chart showing actions taken to modify informationpresented on a display of a defibrillation device based on the detectionof CPR chest compressions. The exemplary process begins at box 602 withcollection of various data during the administration of chestcompressions. The measurements can include measurement of EGC signals,CO2, SpO2, and/or CPR chest compression quality measurements such asdepth, rate, and release information. At box 604, the defibrillatordevice displays CPR information, a filtered ECG waveform, and a secondwaveform such as CO2, SpO2, or chest compressions on the display device.As described above, displaying this combination of information on asingle display device during CPR administration provides an easy to viewsummary of the patient status and CPR quality.

At box 606, the defibrillation device determines whether CPR chestcompressions are still being administered. For example, data collectedfrom an accelerometer can be used to determine whether the rescuer isstill administering chest compressions. If the user is stilladministering chest compressions, the system continues to display boththe CPR information, the filtered ECG waveform, and the second waveform.If the defibrillation device detects that the rescuer has ceasedadministration of chest compressions, at box 608, the defibrillationdevice modifies the information to present on the display and at box 609displays the modified information. An exemplary modification of theinformation presented on the display can include automatically switchingfrom a filtered ECG waveform to an unfiltered ECG waveform upon thedetection of the cessation of chest compressions.

At box 610, the defibrillation device determines whether chestcompressions have been resumed. If chest compressions have not beenresumed, the defibrillation device continues to display the informationfrom the modified display 609. If chest compressions have been resumed,the defibrillation device modifies the display to revert back to showingthe CPR information, filtered ECG waveform, and the CO2 or SpO2waveform.

FIG. 8B shows exemplary information displayed during the administrationof CPR chest compressions while FIGS. 6C and 6D show exemplaryinformation displayed in the absence of CPR chest compressions. Thedefibrillation device automatically switches the information presentedbased on whether chest compressions are detected.

An exemplary modification of the information presented on the displaycan include automatically switching one or more waveforms displayed. Inone example, the type of measurement displayed can be modified based onthe presence or absence of chest compressions. For example, CO2 or depthof chest compressions may be displayed (e.g., a CO2 waveform 620 isdisplayed in FIG. 8B) during CPR administration and upon detection ofthe cessation of chest compressions the waveform can be switched todisplay an SpO2 or pulse waveform (e.g., an SpO2 waveform 622 isdisplayed in FIG. 8C).

Another exemplary modification of the information presented on thedisplay can include automatically adding/removing the CPR informationfrom the display upon detection of the presence or absence of chestcompressions. As shown in FIG. 8B, when chest compressions are detected,a portion 624 of the display includes information about the CPR such asdepth 626, rate 628 and PPI 630. As shown in FIG. 8C, when CPR is haltedand the system detects the absence of CPR chest compressions, thedefibrillation device changes the CPR information in the portion 624 ofthe display to include an indication 632 that the rescuer should resumeCPR and an indication 634 of the idle time since chest compressions werelast detected. In other examples, as shown in FIG. 8D, when CPR ishalted, the defibrillation device can remove the portion of the display624 previously showing CPR data and can display a full view of thesecond waveform. Additionally, information about the idle time 636 canbe presented on another portion of the display.

In some examples, the defibrillator device automatically switchesbetween a filtered and an unfiltered ECG waveform based on the presenceor absence of chest compressions. For example, an ECG waveform withoutfiltering can be displayed when chest compressions are not detectedwhile a filtered ECG waveform can be displayed when chest compressionsare detected. For example, FIG. 8E shows an ECG waveform 640 at the timechest compressions are first initiated. A first portion 644 of the ECGwaveform displays an unfiltered ECG signal. When the defibrillatordevice determines that chest compressions are being performed, thedevice filters the ECG signal and displays a filtered ECG signal asshown in portion 642. FIG. 9A is a flow chart showing actions taken toprovide an indication of CPR quality on a display of a defibrillatordevice. At box 700, during CPR chest compressions the defibrillatordevice analyzes an ECG signal and at box 702 the defibrillator devicecollects information about chest compressions by measuring depth andrate of compressions. The depth and rate of compressions can bedetermined based on measurements collected by an accelerometer. At box704, the defibrillator device displays a filtered ECG signal,information about the depth of CPR chest compressions, and informationabout the rate of CPR chest compressions on a single user interface. Atbox 706, the defibrillator device determines whether the depth and rateof CPR chest compressions are within acceptable ranges by comparing thedepth and rate measurements to threshold values that indicate acceptablevalues for the depth and rate. If the defibrillator device determinesthat the depth and rate are within an acceptable range, thedefibrillator device continues to monitor the quality of chestcompressions. On the other hand, if the defibrillator device determinesthat the depth and rate are outside of the acceptable range, thedefibrillator device modifies the display to provide a visual indicationthat the depth and rate are outside of the acceptable range. The visualindication can be provided in various ways such as a graphicalrepresentation, a highlighting of particular values that are outside ofthe acceptable ranges, and/or a change in the color in which certaininformation is displayed. For example, if the depth or rate is withinthe acceptable range the value could be displayed in green font, if thedepth or rate is near the boundaries of the acceptable range the valuecould be displayed in yellow font, and if the depth or rate is outsideof the acceptable range the value could be displayed in red font. Othercolors or indicators can be used.

FIG. 9B shows exemplary data displayed during the administration of CPRchest compressions when the CPR quality is within acceptable rangeswhile FIG. 9C shows modifications to the display when the CPR quality isoutside of the acceptable range.

In the example shown in FIG. 9C, the rate of chest compressions hasdropped from 154 compressions per minute (FIG. 9B) to 88 compressionsper minute. The defibrillator device determines that the compressionrate of 88 compressions per minute is below the acceptable range of100-200 compressions per minute. In order to alert the user that thecompression rate has fallen below the acceptable range, thedefibrillator device provides a visual indication 718 to emphasize therate information. In this example, the visual indication 718 is ahighlighting of the rate information. Similar visual indications can beprovided based on depth measurements when the depth of the compressionsis more shallow or deeper than an acceptable range of depths.

In the examples shown in FIGS. 9B and 9C, a perfusion performanceindicator (PPI) 716 provides additional information about the quality ofchest compressions during CPR. The PPI 716 includes a shape (e.g., adiamond) with the amount of fill in the shape differing based on themeasured rate and depth of the compressions. In FIG. 9B, the depth andrate fall within the acceptable ranges (e.g., at least 100compressions/minute (CPM) and the depth of each compression is greaterthan 1.5 inches) so the PPI indicator 716 a shows a fully filled shape.In contrast, in FIG. 9C when the rate has fallen below the acceptablerange, the amount of fill in the indicator 716 b is lessened such thatonly a portion of the indicator is filled. The partially filled PPI 716b provides a visual indication of the quality of the CPR is below anacceptable range.

In addition to measuring information about the rate and depth of CPRchest compressions, in some examples the defibrillator device providesinformation about whether the rescuer is fully releasing his/her handsat the end of a chest compression. For example, as a rescuer tires, therescuer may begin leaning on the victim between chest compressions suchthat the chest cavity is not able to fully expand at the end of acompression. If the rescuer does not fully release between chestcompressions the quality of the CPR can diminish. As such, providing avisual or audio indication to the user when the user does not fullyrelease can be beneficial.

FIG. 10A is a flow chart showing actions taken to provide an indicationof whether a rescuer is fully releasing between chest compressions. Atbox 802, the defibrillator device measures depth, rate, and release ofCPR chest compressions. The depth, rate, and release of CPR chestcompressions can be determined based on information collected from anaccelerometer. Based on the collected information, at box 804, thedefibrillator determines whether the rescuer is fully releasing betweenchest compressions. At box 806, the defibrillator provides an indicatoron a display that includes information about whether the rescuer isfully releasing. For example, the display on the defibrillator caninclude a release indication box where the amount of fill in the boxvaries to indicate whether the rescuer is fully releasing between chestcompressions. For example, as shown in FIG. 10B, when the rescuer isfully releasing the box 820 can be fully filled. When the rescuer is notfully releasing the amount of fill in the release indication box isdecreased such that the box is only partially filled (e.g., as shown inbox 822 of FIG. 10C).

As shown in FIG. 11, in some examples, a visual representation of CPRquality in a CPR Compression bar graph 900. The CPR Compression BarGraph 900 can be automatically displayed upon detection of CPR chestcompressions.

In the CPR compression bar graph 900, the extent or height of aparticular bar conveys information about a depth of compression. Forexample, bar 902 has a greater extent than bar 904 indicating that thedepth of the compression associated with bar 902 was greater than thedepth of the compression associated with bar 904. Ranges of preferreddepths can be indicated by horizontally extending lines on the CPRcompression bar graph 900. The lines can provide an indication ofacceptable depths (e.g., region 910) and depths that are too shallow(e.g., region 912). Additionally, compressions falling outside of theacceptable range can be highlighted in a different color thancompressions falling within the acceptable range of compression depth.

In the CPR compression bar graph 900, the y-axis represents time andeach compression is displayed to allow the rescuer to view the rate ofcompressions. For example, region 906 includes closely spaced bars incomparison to region 908 indicating that the rate of chest compressionswas greater in the time period associated with region 906 than in thetime period associated with region 908.

While at least some of the embodiments described above describetechniques and displays used during manual human-delivered chestcompressions, similar techniques and displays can be used with automatedchest compression devices such as the AutoPulse device manufactured byZOLL Medical, Mass.

While at least some of the embodiments described above describetechniques and displays used in conjunction with an AED device, similartechniques and displays can be used with other defibrillator devices.Exemplary professional grade defibrillator devices include the A series,E series or M series devices manufactured by ZOLL Medical, MA and thePhilips MRX or Philips XL devices.

Additionally, the defibrillator may take the form of a wearabledefibrillator such as the LifeVest, manufactured by ZOLL Medical(Chelmsford, Mass.).

Many other implementations other than those described may be employed,and may be encompassed by the following claims.

1. A method for monitoring patient activity using an externaldefibrillator, the method comprising: obtaining data regarding chestcompressions performed on the patient; determining values for depth andrate of a plurality of the chest compressions; displaying on a graphicaldisplay screen of the defibrillator, indications of the determinedvalues for depth and rate.
 2. The method of claim 1, wherein determiningthe values for depth and rate comprises determining numeric values interms of distance for depth and compressions per minute for rate, andwherein displaying the indications of the determined values for depthand rate comprises displaying numbers that correspond to the determinednumeric values.
 3. The method of claim 1, further comprising displayingan icon adjacent the indications of the determined values that indicateswhether the chest compressions are being performed properly.
 4. Themethod of claim 3, wherein a color of the icon changes based on whetherthe chest compressions are being performed properly or improperly. 5.The method of claim 1, further comprising receiving information aboutthe patient's heart activity and displaying on the graphical display,with the determined values for depth and rate, an electrocardiogram ofthe patient.
 6. The method of claim 5, wherein displaying theelectrocardiogram comprises moving an electrocardiogram trace laterallyacross the display
 7. The method of claim 6, further comprisingdisplaying an unfiltered electrocardiogram, sensing that chestcompressions have commenced on the patient, and subsequently displayinga filtered electrocardiogram.
 8. The method of claim 7, furthercomprising momentarily displaying on a trace of the electrocardiogram,an unfiltered portion showing compression artifacts, between anotherunfiltered portion and a filtered portion.
 9. The method of claim 1,further comprising displaying second data from the patient incoordination with the electrocardiogram.
 10. The method of claim 9,further comprising changing a source of the second data in response tosensing that chest compressions have commenced on the patient.
 11. Themethod of claim 10, wherein changing the source of the second datacomprises changing from SPO2 to CO2.
 12. The method of claim 10, whereinchanging the source of the second data comprises changing from a patientchemical measurement to a chest compression measurement.
 13. The methodof claim 12, wherein the chest compression measurement is displayed inthe form of a bar graph.
 14. The method of claim 13, wherein lengths ofbars in the bar graph represent compression depths and spacing of barsin the bar graph represent compression rate.
 15. The method of claim 14,further comprising displaying indicators for standard depth and ratewith the bar graph.
 16. The method of claim 1, wherein obtaining thedata regarding chest compressions performed on the patient comprisesobtaining measurements from an accelerometer that is positioned to movein coordination with the patient's breastbone.
 17. The method of claim16, wherein determining a value for depth comprises double integratingmeasurements from the accelerometer.
 18. The method of claim 1, whereinthe accelerometer is attached to a housing that is in turn attached to apair of defibrillator electrodes to be placed on the patient.
 19. Anexternal defibrillator, comprising: one or more sensors arranged tocontact a patient and obtain measurements regarding chest compressionsperformed on the patient; a video display screen for displayinggraphical representations regarding status of the patient and thedefibrillator to a rescuer; and a processor connected to memory thatstores computer instructions for determining values of depth and rate ofchest compressions performed on the patient and sensed by the sensors,and causing the video display screen to display indications of thedetermined values for depth and rate.
 20. The external defibrillator ofclaim 19, wherein determining the values for depth and rate comprisesdetermining numeric values in terms of distance for depth andcompressions per minute for rate, and wherein displaying the indicationsof the determined values for depth and rate comprises displaying numbersthat correspond to the determined numeric values.
 21. The externaldefibrillator of claim 19, wherein the instructions are further providedto cause the video display screen to display an icon adjacent theindications of the determined values that indicates whether the chestcompressions are being performed properly.
 22. The externaldefibrillator of claim 21, wherein a color of the icon changes based onwhether the chest compressions are being performed properly orimproperly.
 23. The external defibrillator of claim 1, wherein theinstructions are further provided to cause the display on the videodisplay screen an electrocardiogram of the patient with the determinedvalues for depth and rate, in response to receiving information aboutthe patient's heart activity.
 24. The external defibrillator of claim23, wherein displaying the electrocardiogram comprises moving anelectrocardiogram trace laterally across the display
 25. The externaldefibrillator of claim 24, wherein the instructions are further providedto cause the display on the video display screen of an unfilteredelectrocardiogram, and the subsequent display of a filteredelectrocardiogram upon sensing that chest compressions have commenced onthe patient.
 26. The external defibrillator of claim 25, wherein theinstructions are further provided to momentarily display on a trace ofthe electrocardiogram, an unfiltered portion showing compressionartifacts, between another unfiltered portion and a filtered portion.27. The external defibrillator of claim 19, wherein the instructions arefurther provided to display second data from the patient in coordinationwith the electrocardiogram.
 28. The external defibrillator of claim 27,wherein the instructions are further provided to change a source of thesecond data in response to sensing that chest compressions havecommenced on the patient.
 29. The external defibrillator of claim 28,wherein changing the source of the second data comprises changing fromSPO2 to CO2.
 30. The external defibrillator of claim 28, whereinchanging the source of the second data comprises changing from a patientchemical measurement to a chest compression measurement.
 31. Theexternal defibrillator of claim 30, wherein the chest compressionmeasurement is displayed in the form of a bar graph.
 32. The externaldefibrillator of claim 31, wherein lengths of bars in the bar graphrepresent compression depths and spacing of bars in the bar graphrepresent compression rate.
 33. The external defibrillator of claim 32,wherein the instructions are further provided to display indicators forstandard depth and rate with the bar graph.
 34. The externaldefibrillator of claim 19, wherein obtaining the data regarding chestcompressions performed on the patient comprises obtaining measurementsfrom an accelerometer that is positioned to move in coordination withthe patient's breastbone.
 35. The external defibrillator of claim 34,wherein determining a value for depth comprises double integratingmeasurements from the accelerometer.
 36. The external defibrillator ofclaim 19, wherein the one or more sensors comprise an accelerometer thatis attached to a housing that is in turn attached to a pair ofdefibrillator electrodes to be placed on the patient.
 37. An externaldefibrillator, comprising: one or more sensors arranged to contact apatient and obtain measurements regarding chest compressions performedon the patient; a video display screen for displaying graphicalrepresentations regarding status of the patient and the defibrillator toa rescuer; and means for determining values of depth and rate of thechest compressions and for causing the video display screen to displayindications of the determined values for depth and rate in response toreceiving data from the one or more sensors that indicates the depth andrate of the chest compressions.